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Abstract:

To provide a method of manufacturing a crystalline semiconductor film
having a crystal structure with favorable in-plane uniformity. The method
includes: irradiating an amorphous semiconductor film with a
continuous-wave laser beam to increase a temperature of the amorphous
semiconductor film to a range of 600° C. to 1100° C., the
continuous-wave laser beam having a light intensity distribution
continuously convex upward on each of major and minor axes; crystallizing
the amorphous semiconductor film at the temperature increased to the
range of 600° C. to 1100° C.; and increasing a crystal
grain size of the crystallized amorphous semiconductor film, as a result
of an increase in an in-plane temperature of the crystallized amorphous
film to a range of 1100° C. to 1414° C. by latent heat
released in the crystallizing of the amorphous semiconductor film.

Claims:

1. A method of manufacturing a crystalline semiconductor film, said
method comprising: irradiating an amorphous semiconductor film with a
continuous-wave laser beam to increase a temperature of the amorphous
semiconductor film to a range of 600.degree. C. to 1100.degree. C., the
continuous-wave laser beam having a light intensity distribution which is
continuously convex upward on each of major and minor axes; crystallizing
the amorphous semiconductor film irradiated with the continuous-wave
laser beam in said irradiating, at the temperature increased to the range
of 600.degree. C. to 1100.degree. C.; and increasing a crystal grain size
of the crystallized amorphous semiconductor film, as a result of an
increase in an in-plane temperature of the crystallized amorphous film to
a range of 1100.degree. C. to 1414.degree. C. by latent heat released in
said crystallizing of the amorphous semiconductor film irradiated with
the continuous-wave laser beam, wherein the light intensity distribution
continuously convex upward has a width where a light intensity is equal
to or higher than a predetermined intensity in a major axis direction,
and the width corresponds to a width of an area included in the amorphous
semiconductor film and increased in temperature to the range of
1100.degree. C. to 1414.degree. C. by the latent heat.

2. The method of manufacturing a crystalline semiconductor film according
to claim 1, wherein the light intensity distribution which is
continuously convex upward is a Gaussian distribution.

3. The method of manufacturing a crystalline semiconductor film according
to claim 1, wherein, in said irradiating, the amorphous semiconductor
film is irradiated with the continuous-wave laser beam so that the
temperature of the amorphous semiconductor film is in a range of
600.degree. C. to 800.degree. C.

4. The method of manufacturing a crystalline semiconductor film according
to claim 1, wherein, in said irradiating, the amorphous semiconductor
film is irradiated with the continuous-wave laser beam for a period of
time on the order of microseconds.

5. The method of manufacturing a crystalline semiconductor film according
to claim 4, wherein, in said irradiating, the amorphous semiconductor
film is irradiated with the continuous-wave laser beam for 10
microseconds to 100 microseconds.

6. The method of manufacturing a crystalline semiconductor film according
to claim 1, said method further comprising, prior to said irradiating:
preparing a base material; arranging a plurality of gate electrodes at
predetermined intervals above the base material; forming an insulating
film over the gate electrodes arranged at the predetermined intervals;
and forming the amorphous semiconductor film on the insulating film,
wherein a certain width of the light intensity distribution is defined in
the major axis direction to increase, to the range of 1100.degree. C. to
1414.degree. C. by the latent heat, a temperature of the area which is
included in the amorphous semiconductor film and positionally corresponds
to the gate electrodes arranged at the predetermined intervals.

7. The method of manufacturing a crystalline semiconductor film according
to claim 6, wherein the width of the area which is included in the
amorphous semiconductor film and positionally corresponds to the gate
electrodes arranged at the predetermined intervals is wider than a width
of each of the gate electrodes.

8. A substrate coated with a crystalline semiconductor film, said
substrate comprising: a base material; a plurality of gate electrodes
arranged above said base material; an insulating film formed over said
gate electrodes; and a crystalline semiconductor film formed to cover
said insulating film formed over the gate electrodes arranged above said
base material, wherein said crystalline semiconductor film includes: a
first area formed from crystal grains with an average size of 40 nm to 60
nm and seamlessly formed over an area where said gate electrodes are
arranged; and a second area formed from crystal grains with an average
size of 25 nm to 35 nm and located adjacent to the first area.

9. The substrate coated with the crystalline semiconductor film according
to claim 8, wherein said crystalline semiconductor film includes a mixed
amorphous-crystalline crystal.

10. The substrate coated with the crystalline semiconductor film
according to claim 8, wherein said gate electrodes are arranged in a row,
above said base material, and the first area included in said crystalline
semiconductor film and formed from the crystal grains with the average
size of 40 nm to 60 nm is in a seamless belt-like shape and formed over
the area where said gate electrodes are arranged in the row.

11. The substrate coated with the crystalline semiconductor film
according to claim 8, wherein the first area included in said crystalline
semiconductor film and formed from the crystal grains with the average
size of 40 nm to 60 nm is formed by: irradiating an amorphous
semiconductor film with a continuous-wave laser beam to increase a
temperature of the amorphous semiconductor film to a range of 600.degree.
C. to 800.degree. C., the continuous-wave laser beam having a light
intensity distribution which is continuously convex upward on each of
major and minor axes; crystallizing the amorphous semiconductor film
irradiated with the continuous-wave laser beam in said irradiating, at
the temperature increased to the range of 600.degree. C. to 800.degree.
C.; and increasing a crystal grain size of the crystallized amorphous
semiconductor film, as a result of an increase in an in-plane temperature
of the crystallized amorphous film to a range of 1100.degree. C. to
1414.degree. C. by latent heat released in said crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
is defined on the major axis to ensure a certain width of an area
included in the amorphous semiconductor film and increased in temperature
to the range of 1100.degree. C. to 1414.degree. C. by the latent heat,
and the area included in the amorphous semiconductor film and increased
in temperature to the range of 1100.degree. C. to 1414.degree. C. by the
latent heat corresponds to the first area.

12. A bottom-gate thin-film transistor comprising: a gate electrode; an
insulating film formed on said gate electrode; a crystalline
semiconductor film formed on said insulating film; and a source-drain
electrode formed on said crystalline semiconductor film, wherein said
crystalline semiconductor film is formed from crystal grains with an
average size of 40 nm to 60 nm, and each of the crystal grains are formed
by: irradiating an amorphous semiconductor film with a continuous-wave
laser beam to increase a temperature of the amorphous semiconductor film
to a range of 600.degree. C. to 800.degree. C., the continuous-wave laser
beam having a light intensity distribution which is continuously convex
upward on each of major and minor axes; crystallizing the amorphous
semiconductor film irradiated with the continuous-wave laser beam in said
irradiating, at the temperature increased to the range of 600.degree. C.
to 800.degree. C.; and increasing a crystal grain size of the
crystallized amorphous semiconductor film, as a result of an increase in
an in-plane temperature of the crystallized amorphous film to a range of
1100.degree. C. to 1414.degree. C. by latent heat released in said
crystallizing of the amorphous semiconductor film irradiated with the
continuous-wave laser beam, wherein the light intensity distribution
continuously convex upward is defined on the major axis to ensure a
certain width of an area included in the amorphous semiconductor film and
increased in temperature to the range of 1100.degree. C. to 1414.degree.
C. by the latent heat.

13. A substrate coated with a crystalline semiconductor film, said
substrate comprising: a base material; a plurality of source-drain
electrodes arranged above said base material; an insulating film formed
over the source-drain electrodes; and a crystalline semiconductor film
formed to cover said insulating film formed over the source-drain
electrodes arranged above said base material, wherein said crystalline
semiconductor film includes: a first area formed from crystal grains with
an average size of 40 nm to 60 nm and seamlessly formed over an area
where said source-drain electrodes are arranged; and a second area formed
from crystal grains with an average size of 25 nm to 35 nm and located
adjacent to the first area.

14. The substrate coated with the crystalline semiconductor film
according to claim 13, wherein said crystalline semiconductor film
includes a mixed amorphous-crystalline crystal.

15. The substrate coated with the crystalline semiconductor film
according to claim 13, wherein said gate electrodes are arranged in a
row, above said base material, and the first area included in said
crystalline semiconductor film and formed from the crystal grains with
the average size of 40 nm to 60 nm is in a seamless belt-like shape and
formed over the area where said gate electrodes are arranged in the row.

16. The substrate coated with the crystalline semiconductor film
according to claim 13, wherein the first area included in said
crystalline semiconductor film and formed from the crystal grains with
the average size of 40 nm to 60 nm is formed by: irradiating an amorphous
semiconductor film with a continuous-wave laser beam to increase a
temperature of the amorphous semiconductor film to a range of 600.degree.
C. to 800.degree. C., the continuous-wave laser beam having a light
intensity distribution which is continuously convex upward on each of
major and minor axes; crystallizing the amorphous semiconductor film
irradiated with the continuous-wave laser beam in said irradiating, at
the temperature increased to the range of 600.degree. C. to 800.degree.
C.; and increasing a crystal grain size of the crystallized amorphous
semiconductor film, as a result of an increase in an in-plane temperature
of the crystallized amorphous film to a range of 1100.degree. C. to
1414.degree. C. by latent heat released in said crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
is defined on the major axis to ensure a certain width of an area
included in the amorphous semiconductor film and increased in temperature
to the range of 1100.degree. C. to 1414.degree. C. by the latent heat,
and the area included in the amorphous semiconductor film and increased
in temperature to the range of 1100.degree. C. to 1414.degree. C. by the
latent heat corresponds to the first area.

17. A top-gate thin-film transistor comprising: a source-drain electrode;
a crystalline semiconductor film formed on said source-drain electrode;
an insulating film formed on said crystalline semiconductor film; and a
gate electrode formed on said insulating film, wherein said crystalline
semiconductor film is formed from crystal grains with an average size of
40 nm to 60 nm, and each of the crystal grains are formed by: irradiating
an amorphous semiconductor film with a continuous-wave laser beam to
increase a temperature of the amorphous semiconductor film to a range of
600.degree. C. to 800.degree. C., the continuous-wave laser beam having a
light intensity distribution which is continuously convex upward on each
of major and minor axes; crystallizing the amorphous semiconductor film
irradiated with the continuous-wave laser beam in said irradiating, at
the temperature increased to the range of 600.degree. C. to 800.degree.
C.; and increasing a crystal grain size of the crystallized amorphous
semiconductor film, as a result of an increase in an in-plane temperature
of the crystallized amorphous film to a range of 1100.degree. C. to
1414.degree. C. by latent heat released in said crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
is defined on the major axis to ensure a certain width of an area
included in the amorphous semiconductor film and increased in temperature
to the range of 1100.degree. C. to 1414.degree. C. by the latent heat.

18. A method of manufacturing a crystalline semiconductor film, said
method comprising: irradiating an amorphous semiconductor film with a
continuous-wave laser beam to increase a temperature of the amorphous
semiconductor film to a first temperature which is lower than a melting
point of the amorphous semiconductor film and at which the amorphous
semiconductor film is crystallized by a solid phase growth mechanism, the
continuous-wave laser beam having a light intensity distribution which is
continuously convex upward on each of major and minor axes; crystallizing
the amorphous semiconductor film irradiated with the continuous-wave
laser beam in said irradiating, at the first temperature; and increasing
a crystal grain size of the crystallized amorphous semiconductor film, as
a result of an increase in an in-plane temperature of the crystallized
amorphous semiconductor film to a second temperature by latent heat
released in said crystallizing of the amorphous semiconductor film
irradiated with the continuous-wave laser beam, the second temperature
ranging from the melting point of the amorphous semiconductor film to a
crystalline melting point, wherein the light intensity distribution
continuously convex upward has a width where a light intensity is equal
to or higher than a predetermined intensity in a major axis direction,
and the width corresponds to a width of an area included in the amorphous
semiconductor film and increased in temperature to the second temperature
by the latent heat.

19. A bottom-gate thin-film transistor comprising: a gate electrode; an
insulating film formed on said gate electrode; a crystalline
semiconductor film formed on said insulating film; and a source-drain
electrode formed on said crystalline semiconductor film, wherein said
crystalline semiconductor film is formed from crystal grains with an
average size of 40 nm to 60 nm, and each of the crystal grains are formed
by: irradiating an amorphous semiconductor film with a continuous-wave
laser beam to increase a temperature of the amorphous semiconductor film
to a first temperature which is lower than a melting point of the
amorphous semiconductor film and at which the amorphous semiconductor
film is crystallized by a solid phase growth mechanism, the
continuous-wave laser beam having a light intensity distribution which is
continuously convex upward on each of major and minor axes; crystallizing
the amorphous semiconductor film irradiated with the continuous-wave
laser beam in said irradiating, at the first temperature; and increasing
a crystal grain size of the crystallized amorphous semiconductor film, as
a result of an increase in an in-plane temperature of the crystallized
amorphous semiconductor film to a second temperature by latent heat
released in said crystallizing of the amorphous semiconductor film
irradiated with the continuous-wave laser beam, the second temperature
ranging from the melting point of the amorphous semiconductor film to a
crystalline melting point, wherein the light intensity distribution
continuously convex upward is defined on the major axis to ensure a
certain width of an area included in the amorphous semiconductor film and
increased to the second temperature by the latent heat.

20. A top-gate thin-film transistor comprising: a source-drain electrode;
a crystalline semiconductor film formed on said source-drain electrode;
an insulating film formed on said crystalline semiconductor film; and a
gate electrode formed on said insulating film, wherein said crystalline
semiconductor film is formed from crystal grains with an average size of
40 nm to 60 nm, and each of the crystal grains are formed by: irradiating
an amorphous semiconductor film with a continuous-wave laser beam to
increase a temperature of the amorphous semiconductor film to a first
temperature which is lower than a melting point of the amorphous
semiconductor film and at which the amorphous semiconductor film is
crystallized by a solid phase growth mechanism, the continuous-wave laser
beam having a light intensity distribution which is continuously convex
upward on each of major and minor axes; crystallizing the amorphous
semiconductor film irradiated with the continuous-wave laser beam in said
irradiating, at the first temperature; and increasing a crystal grain
size of the crystallized amorphous semiconductor film, as a result of an
increase in an in-plane temperature of the crystallized amorphous
semiconductor film to a second temperature by latent heat released in
said crystallizing of the amorphous semiconductor film irradiated with
the continuous-wave laser beam, the second temperature ranging from the
melting point of the amorphous semiconductor film to a crystalline
melting point, wherein the light intensity distribution continuously
convex upward is defined on the major axis to ensure a certain width of
an area included in the amorphous semiconductor film and increased to the
second temperature by the latent heat.

Description:

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation application of PCT application No.
PCT/JP2010/003157 filed on May 10, 2010, designating the United States of
America.

BACKGROUND OF THE INVENTION

[0002] (1) Field of the Invention

[0003] The present invention relates to a method of manufacturing a
crystalline semiconductor film, a method of manufacturing a substrate
coated with a crystalline semiconductor film, and a thin-film transistor.

[0004] (2) Description of the Related Art

[0005] Examples used for manufacturing a liquid crystal panel or an
organic electroluminescence (EL) panel designed for a display device
include a thin-film transistor (TFT). A semiconductor layer which is made
of, for example, silicon and serves as a channel part of the thin-film
transistor is formed, in general, from an amorphous semiconductor film or
a crystalline semiconductor film. It is preferable that a semiconductor
film serving as the channel part of the thin-film transistor be formed
from a crystalline semiconductor film, which has a higher mobility as
compared with amorphous silicon. Generally speaking, an amorphous
semiconductor film is firstly formed, and then a crystalline
semiconductor film is formed as a result of crystallizing the amorphous
semiconductor film.

[0006] Examples of the methods of manufacturing a crystalline
semiconductor film from an amorphous semiconductor film include: excimer
laser annealing (ELA); thermal annealing crystallization using a nickel
(Ni) catalyst or the like; and crystallization using a combination of an
infrared semiconductor laser light and a sample structure having a
light-absorbing layer.

[0007] In the case of crystallization according to the ELA method, since a
crystalline semiconductor film is formed from microcrystals or
polycrystals, electrical characteristics of the crystalline semiconductor
film vary according to the size and distribution of crystal grains
(crystal structure). For this reason, when crystalline semiconductor
films are used for manufacturing thin-film transistors, the
characteristic variation occurs among the thin-film transistors.

[0008] In the case of thermal annealing crystallization, although uniform
crystallization can be achieved, it is difficult to process catalyst
metals. In the case of crystallization using the combination of an
infrared semiconductor laser light and a sample structure having a
light-absorbing layer, a process is required to form a film from a
light-absorbing layer and a buffer layer as samples and then perform
removal, which leads to a problem in terms of tact. Moreover, a thin-film
transistor manufactured using a film crystallized using one of these
solid phase growth techniques has a problem of not achieving target
electrical characteristics due to a small average grain size of the film.

[0009] To address this problem, Japanese Unexamined Patent Application
Publication No. 2008-85317 (referred to as Patent Reference 1 hereafter)
discloses a technique capable of controlling a crystal grain size of a
crystalline semiconductor film included in a thin-film transistor.
Moreover, Japanese Unexamined Patent Application Publication No.
2008-85318 (referred to as Patent Reference 2 hereafter) discloses a
technique capable of controlling a grain boundary direction and a crystal
grain size of a crystalline semiconductor film included in a thin-film
transistor.

[0010] The techniques disclosed by Patent References 1 and 2 can form a
crystalline semiconductor film having a large grain size of 0.5 μm to
10 μm by growing crystals in a predetermined direction using a laser
beam. Moreover, using a semiconductor element made from such a film, an
excellent semiconductor device can be manufactured which has less
variation between adjacent crystals.

SUMMARY OF THE INVENTION

[0011] However, each of Patent References 1 and 2 only discloses the
technique to form a crystalline semiconductor film having large crystal
grains.

[0012] The ELA method crystallizes an amorphous semiconductor film using a
pulsed laser beam, such as a xenon chlorine (XeCl) excimer laser beam
whose wavelength λ is 308 nm. To be more specific, the temperature
of the amorphous semiconductor film is increased instantaneously by the
pulsed excimer laser beam (an irradiation time is on the order of
nanoseconds). As a result, the amorphous semiconductor film is melted and
then crystallized. Here, as mentioned, the pulsed excimer laser beam is
applied for a period of time as short as nanoseconds. Although the
amorphous semiconductor film is crystallized only after being melted at
the melting point of a semiconductor film (silicon) (i.e., 1414°
C.) or higher, the crystal grain size varies depending on a condition.
Moreover, a volume expansion in a crystallization process of the
amorphous semiconductor film, that is, the volume expansion from liquid
(in the melted state) to solid (in the crystallized state) causes
protrusions on the surface of the crystallized crystalline semiconductor
film, resulting in a loss of flatness. In other words, in-plane variation
is caused in the grain size of the crystalline semiconductor film. This
variation becomes a problem in a process, such as an etching process, to
manufacture a thin-film transistor. Also, a multiple number of beam shots
are required to counter the in-plane variation of the crystallized
crystalline semiconductor film, and this leads to a problem in terms of
cost and tact.

[0013] Moreover, when a voltage is applied to, for example, a gate
electrode of a thin-film transistor having such a crystalline
semiconductor film, the amount of current flowing between a source and a
drain varies. Suppose, for example, that a current-driven display device,
such as an organic EL display device, includes the above thin-film
transistor. In this case, since the gradation of the organic EL is
controlled by the current, the variation in the amount of current
directly leads to the variation in displayed images. Thus, a
high-precision image cannot be obtained. Also, the protrusions on the
surface of the crystalline semiconductor film result in leakage current
between the source and the drain, thereby deteriorating the
characteristics of the thin-film transistor.

[0014] Although Patent References 1 and 2 disclose the techniques to
control the grain size in order to address the aforementioned problem of
the ELA method, the problem caused by the surface protrusions is not
solved and is not even mentioned by Patent References 1 and 2.

[0015] The present invention is conceived in view of the stated problem,
and has an object to provide a method of manufacturing a crystalline
semiconductor film having a crystal structure with favorable in-plane
uniformity, a method of manufacturing a substrate coated with a
crystalline semiconductor film, and a thin-film transistor.

[0016] In order to achieve the aforementioned object, the method of
manufacturing the crystalline semiconductor film according to an aspect
of the present invention includes: irradiating an amorphous semiconductor
film with a continuous-wave laser beam to increase a temperature of the
amorphous semiconductor film to a range of 600° C. to 1100°
C., the continuous-wave laser beam having a light intensity distribution
which is continuously convex upward on each of major and minor axes;
crystallizing the amorphous semiconductor film irradiated with the
continuous-wave laser beam in the irradiating, at the temperature
increased to the range of 600° C. to 1100° C.; and
increasing a crystal grain size of the crystallized amorphous
semiconductor film, as a result of an increase in an in-plane temperature
of the crystallized amorphous film to a range of 1100° C. to
1414° C. by latent heat released in the crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
has a width where a light intensity is equal to or higher than a
predetermined intensity in a major axis direction, and the width
corresponds to a width of an area included in the amorphous semiconductor
film and increased in temperature to the range of 1100° C. to
1414° C. by the latent heat.

[0017] The present invention can implement a method of manufacturing a
crystalline semiconductor film having a crystal structure with favorable
in-plane uniformity, a method of manufacturing a substrate coated with a
crystalline semiconductor film, and a thin-film transistor.

FURTHER INFORMATION ABOUT TECHNICAL BACKGROUND TO THIS APPLICATION

[0018] The disclosure of PCT application No. PCT/JP2010/003157 filed on
May 10, 2010, including specification, drawings and claims is
incorporated herein by reference in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] These and other objects, advantages and features of the invention
will become apparent from the following description thereof taken in
conjunction with the accompanying drawings that illustrate a specific
embodiment of the invention. In the Drawings:

[0020] FIG. 1 is a diagram showing an example of a configuration of a
continuous-wave (CW) laser crystallization device in a first embodiment;

[0021] FIG. 2A is a diagram showing a minor-axis profile of a CW laser
beam in the first embodiment;

[0022]FIG. 2B is a diagram showing a major-axis profile of the CW laser
beam in the first embodiment;

[0023]FIG. 3A is a diagram showing a minor-axis profile of a CW laser
beam;

[0024]FIG. 3B is a diagram showing a major-axis profile of the CW laser
beam;

[0025]FIG. 4 is a diagram explaining a problem in crystallization
performed using a longitudinal flat-top beam;

[0026] FIG. 5A is a diagram showing an example of a crystal structure
resulting from solid phase crystallization (SPC);

[0027] FIG. 5B is a diagram showing an example of a crystal structure
resulting from crystallization performed using the CW laser beam in the
first embodiment;

[0028] FIG. 5C is a diagram showing, for comparison, an example of a
crystal structure of polycrystalline silicon formed by furnace annealing
or the like;

[0029]FIG. 6 is a diagram showing a relationship between temperature and
energy in silicon crystallization;

[0030]FIG. 7 is a diagram explaining a growth mechanism of a crystal
structure resulting from explosive nucleation (Ex);

[0031]FIG. 8 is a diagram explaining crystallization performed using the
CW laser beam in the first embodiment;

[0032] FIG. 9 is a diagram explaining an example of the application of the
crystalline semiconductor film to a substrate, in a second embodiment;

[0033] FIG. 10 is a diagram explaining a method of manufacturing a
bottom-gate thin-film transistor in the second embodiment;

[0034]FIG. 11 is a flowchart explaining the method of manufacturing the
bottom-gate thin-film transistor in the second embodiment;

[0035] FIG. 12 is a diagram showing a configuration of the bottom-gate
thin-film transistor including the crystalline semiconductor film, in the
second embodiment;

[0036]FIG. 13 is a diagram explaining the case where a plurality of
bottom-gate thin-film transistors are manufactured at one time;

[0037]FIG. 14 is a diagram explaining a method of manufacturing a
top-gate thin-film transistor in a third embodiment;

[0038] FIG. 15 is a diagram showing a configuration of a top-gate
thin-film transistor in the third embodiment;

[0039]FIG. 16 is a diagram showing another configuration of a top-gate
thin-film transistor in the third embodiment; and

[0040]FIG. 17 is a flowchart explaining the method of manufacturing the
top-gate thin-film transistor in the third embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] The method of manufacturing the crystalline semiconductor film
according to an aspect of the present invention includes: irradiating an
amorphous semiconductor film with a continuous-wave laser beam to
increase a temperature of the amorphous semiconductor film to a range of
600° C. to 1100° C., the continuous-wave laser beam having
a light intensity distribution which is continuously convex upward on
each of major and minor axes; crystallizing the amorphous semiconductor
film irradiated with the continuous-wave laser beam in the irradiating,
at the temperature increased to the range of 600° C. to
1100° C.; and increasing a crystal grain size of the crystallized
amorphous semiconductor film, as a result of an increase in an in-plane
temperature of the crystallized amorphous film to a range of 1100°
C. to 1414° C. by latent heat released in the crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
has a width where a light intensity is equal to or higher than a
predetermined intensity in a major axis direction, and the width
corresponds to a width of an area included in the amorphous semiconductor
film and increased in temperature to the range of 1100° C. to
1414° C. by the latent heat.

[0042] For example, a continuous-wave (CW) laser beam, such as a green
laser light or a blue laser light, is emitted for a relatively long
period of time of 10 microseconds to 100 microseconds, instead of a short
period of time of 10 nanoseconds to 100 nanoseconds. According to the
present aspect, the amorphous semiconductor film is irradiated at a power
density such that the temperature of the amorphous semiconductor film is
in a range of 600° C. to 1100° C. With the irradiation that
instantaneously increases the temperature of the amorphous semiconductor
film into the range of 600° C. to 1100° C., the temperature
of the amorphous semiconductor film is further increased by latent heat
of crystallization. Thus, the amorphous semiconductor film reaches a
temperature: which is higher than a temperature considered to be the
melting point of amorphous silicon that varies depending on an atomic
network structure of amorphous silicon; and which is equal to or lower
than the melting point of crystalline silicon, i.e., 1414° C. As a
result, the crystal grain size is slightly increased as compared with the
size of a crystal obtained by the solid phase growth mechanism, and the
uniformity is maintained as well. Moreover, no surface protrusions are
caused. Accordingly, the amorphous semiconductor film is formed into a
crystalline semiconductor film which is of high quality in manufacturing,
for example, a thin-film transistor. With this, the characteristics of a
thin-film transistor device including the aforementioned semiconductor
film can be enhanced, by preventing surface protrusions and maintaining
the surface flatness of the semiconductor film.

[0043] In this way, the method of manufacturing the crystalline
semiconductor film having a crystal structure with favorable in-plane
uniformity can be implemented.

[0044] Here, the light intensity distribution which is continuously convex
upward is a Gaussian distribution.

[0045] In the irradiating, the amorphous semiconductor film is irradiated
with the continuous-wave laser beam so that the temperature of the
amorphous semiconductor film is in a range of 600° C. to
800° C.

[0046] According to the present aspect, when the temperature range of the
amorphous semiconductor film is from 600° C. to 800° C. in
the irradiating, the same advantageous effect can be achieved as in the
case where the temperature range is from 600° C. to 1100°
C.

[0047] Moreover, in the irradiating, the amorphous semiconductor film is
irradiated with the continuous-wave laser beam for a period of time on
the order of microseconds.

[0048] According to the present aspect, the amorphous semiconductor film
can be irradiated with the CW laser beam for a longer time. This can
secure sufficient time for the atomic structure of the amorphous
semiconductor film to crystallize from the amorphous state and for the
atoms to rearrange themselves from the amorphous state.

[0049] Moreover, in the irradiating, the amorphous semiconductor film is
irradiated with the continuous-wave laser beam for 10 microseconds to 100
microseconds.

[0050] According to this aspect, the amorphous semiconductor film can be
irradiated with the CW laser beam for a longer time. This can secure
sufficient time for the atoms on the amorphous semiconductor film to
rearrange themselves to crystallize from the amorphous state.

[0051] Furthermore, the method includes, prior to the irradiating:
preparing a base material; arranging a plurality of gate electrodes at
predetermined intervals above the base material; forming an insulating
film over the gate electrodes arranged at the predetermined intervals;
and forming the amorphous semiconductor film on the insulating film,
wherein a certain width of the light intensity distribution is defined in
the major axis direction to increase, to the range of 1100° C. to
1414° C. by the latent heat, a temperature of the area which is
included in the amorphous semiconductor film and positionally corresponds
to the gate electrodes arranged at the predetermined intervals.

[0052] In the present aspect, the width of the Gaussian distribution of
the CW laser beam in the major axis direction corresponds to the width of
the area which is included in the amorphous semiconductor film and
positionally corresponds to the gate electrodes arranged at the
predetermined intervals. Thus, the area which positionally corresponds to
the gate electrodes can be selectively irradiated, meaning that an area
included in the crystalline semiconductor film to be formed as a channel
part of the thin-film transistor can be selectively micro-crystallized.
As a result, a flat-surface crystalline semiconductor film can be formed
as the channel part.

[0053] Moreover, the width of the area which is included in the amorphous
semiconductor film and positionally corresponds to the gate electrodes
arranged at the predetermined intervals may be wider than a width of each
of the gate electrodes.

[0054] The substrate coated with a crystalline semiconductor film in
another aspect according to the present invention includes: a base
material; a plurality of gate electrodes arranged above the base
material; an insulating film formed over the gate electrodes; and a
crystalline semiconductor film formed to cover the insulating film formed
over the gate electrodes arranged above the base material, wherein the
crystalline semiconductor film includes: a first area formed from crystal
grains with an average size of 40 nm to 60 nm and seamlessly formed over
an area where the gate electrodes are arranged; and a second area formed
from crystal grains with an average size of 25 nm to 35 nm and located
adjacent to the first area.

[0055] According to the present aspect, the first area included in the
crystalline semiconductor film and formed from the crystal grains whose
average size is 40 nm to 60 nm is seamlessly formed on the area where the
gate electrodes are arranged. The thin-film transistor manufactured using
such a crystalline semiconductor film can secure the mobility to obtain
adequate ON characteristics as the thin-film transistor to be used in an
organic EL display device.

[0056] Moreover, the crystalline semiconductor film may include a mixed
amorphous-crystalline crystal.

[0057] For example, the crystalline semiconductor film includes a mixed
amorphous-crystalline crystal. That is, the mixed crystal includes a
crystal grain with the average size of 40 nm to 60 nm and an amorphous
area around the crystal gain. This structure can reduce the surface
roughness.

[0058] Furthermore, the gate electrodes may be arranged in a row, above
the base material, and the first area included in the crystalline
semiconductor film and formed from the crystal grains with the average
size of 40 nm to 60 nm may be in a seamless belt-like shape and formed
over the area where the gate electrodes are arranged in the row.

[0059] According to the present aspect, the first area included in the
crystalline semiconductor film and formed from the crystal grains whose
average size is 40 nm to 60 nm is seamlessly formed on the area where the
gate electrodes are arranged. The substrate coated with the crystalline
semiconductor film in the present aspect can be divided into multiple
pieces along the aforementioned belt-like area according to the dicing
method or the like. Thus, the present aspect can implement the substrate
coated with the semiconductor film which can be easily divided into
multiple pieces according to the dicing method or the like.

[0060] Moreover, the first area included in the crystalline semiconductor
film and formed from the crystal grains with the average size of 40 nm to
60 nm may be formed by: irradiating an amorphous semiconductor film with
a continuous-wave laser beam to increase a temperature of the amorphous
semiconductor film to a range of 600° C. to 800° C., the
continuous-wave laser beam having a light intensity distribution which is
continuously convex upward on each of major and minor axes; crystallizing
the amorphous semiconductor film irradiated with the continuous-wave
laser beam in the irradiating, at the temperature increased to the range
of 600° C. to 800° C.; and increasing a crystal grain size
of the crystallized amorphous semiconductor film, as a result of an
increase in an in-plane temperature of the crystallized amorphous film to
a range of 1100° C. to 1414° C. by latent heat released in
the crystallizing of the amorphous semiconductor film irradiated with the
continuous-wave laser beam, wherein the light intensity distribution
continuously convex upward is defined on the major axis to ensure a
certain width of an area included in the amorphous semiconductor film and
increased in temperature to the range of 1100° C. to 1414°
C. by the latent heat, and the area included in the amorphous
semiconductor film and increased in temperature to the range of
1100° C. to 1414° C. by the latent heat corresponds to the
first area.

[0061] For example, in the irradiating according to the present aspect,
the CW laser beam, such as a green laser light or a blue laser light, is
emitted to the amorphous semiconductor film for a period of time on the
order of microseconds, instead of the order of nanoseconds, to increase
the temperature of the amorphous semiconductor film into the range of
600° C. to 800° C. In the irradiating, when the entire
surface of the amorphous semiconductor film is irradiated so that the
temperature of the amorphous semiconductor film is in the range of
600° C. to 800° C., crystallization is also achieved at
1414° C. or lower by the latent heat caused to the amorphous
semiconductor film. As a result, the size of crystal grains is relatively
small and no surface protrusions are formed, thereby leading to no
problem.

[0062] In the crystallizing, the amorphous semiconductor film is
irradiated so that the temperature of the amorphous semiconductor film is
in the range of 600° C. to 800° C., instead of the range of
1100° C. to 1414° C. With this irradiation, the temperature
of the amorphous semiconductor film is increased to the range of
1100° C. to 1414° C. by the latent heat caused to the
amorphous semiconductor film.

[0063] In the increasing following the crystallizing, since the amorphous
semiconductor film is melted to crystallize at a temperature of
1414° C. or lower, the average size of crystal grains is 40 nm to
60 nm which is relatively small. Also, no protrusions are caused on the
surface of the crystalline semiconductor film formed by the
crystallization as described and, therefore, the surface flatness of the
crystalline semiconductor film can be maintained. This can enhance the
characteristics of the thin-film transistor including this crystalline
semiconductor film.

[0064] It should be noted that, when the irradiation is performed so that
the temperature of the entire surface of the amorphous semiconductor film
is in the range of 1100° C. to 1414° C., the latent heat
caused to the amorphous semiconductor film may develop an area whose
temperature is higher than 1414° C. in the amorphous semiconductor
film. The amorphous semiconductor film crystallized while including the
area with the temperature higher than 1414° C. may end up having a
surface protrusion of, for example, 50 nm which is identical in length to
the thickness of the amorphous semiconductor film.

[0065] As described, according to the present aspect, the amorphous
semiconductor film is irradiated with the laser beam so that the
temperature of the amorphous semiconductor film is in the range of
600° C. to 800° C. With this irradiation, the temperature
of the amorphous semiconductor film is increased to the range of
1100° C. to 1414° C. by the latent heat, and the amorphous
semiconductor film is accordingly crystallized. Thus, the amorphous
semiconductor film has no area crystallized at a temperature higher than
1414° C. As a result, the crystalline semiconductor film having no
surface protrusions and maintaining the surface flatness can be formed.
Also, the substrate coated with this crystalline semiconductor film can
be implemented.

[0066] The thin-film transistor in an aspect according to the present
invention is a bottom-gate thin-film transistor including: a gate
electrode; an insulating film formed on the gate electrode; a crystalline
semiconductor film formed on the insulating film; and a source-drain
electrode formed on the crystalline semiconductor film, wherein the
crystalline semiconductor film is formed from crystal grains with an
average size of 40 nm to 60 nm, and each of the crystal grains are formed
by: irradiating an amorphous semiconductor film with a continuous-wave
laser beam to increase a temperature of the amorphous semiconductor film
to a range of 600° C. to 800° C., the continuous-wave laser
beam having a light intensity distribution which is continuously convex
upward on each of major and minor axes; crystallizing the amorphous
semiconductor film irradiated with the continuous-wave laser beam in the
irradiating, at the temperature increased to the range of 600° C.
to 800° C.; and increasing a crystal grain size of the
crystallized amorphous semiconductor film, as a result of an increase in
an in-plane temperature of the crystallized amorphous film to a range of
1100° C. to 1414° C. by latent heat released in the
crystallizing of the amorphous semiconductor film irradiated with the
continuous-wave laser beam, wherein the light intensity distribution
continuously convex upward is defined on the major axis to ensure a
certain width of an area included in the amorphous semiconductor film and
increased in temperature to the range of 1100° C. to 1414°
C. by the latent heat.

[0067] According to the present aspect, the amorphous semiconductor film
is irradiated with the laser beam so that the temperature of the
amorphous semiconductor film is in the range of 600° C. to
800° C. With this irradiation, the temperature of the amorphous
semiconductor film is increased to the range of 1100° C. to
1414° C. by the latent heat, and the amorphous semiconductor film
is accordingly crystallized. Thus, the amorphous semiconductor film has
no area crystallized at a temperature higher than 1414° C. As a
result, the crystalline semiconductor film having no surface protrusions
and maintaining the surface flatness can be formed. Also, the thin-film
transistor having this crystalline semiconductor film can be implemented.

[0068] The substrate coated with a crystalline semiconductor film in an
aspect according to the present invention includes: a base material; a
plurality of source-drain electrodes arranged above the base material; an
insulating film formed over the source-drain electrodes; and a
crystalline semiconductor film formed to cover the insulating film formed
over the source-drain electrodes arranged above the base material,
wherein the crystalline semiconductor film includes: a first area formed
from crystal grains with an average size of 40 nm to 60 nm and seamlessly
formed over an area where the source-drain electrodes are arranged; and a
second area formed from crystal grains with an average size of 25 nm to
35 nm and located adjacent to the first area.

[0069] According to the present aspect, the first area included in the
crystalline semiconductor film and formed from the crystal grains whose
average size is 40 nm to 60 nm is seamlessly formed on the area where the
gate electrodes are arranged. The thin-film transistor manufactured using
such a crystalline semiconductor film can secure the mobility to obtain
adequate ON characteristics as the thin-film transistor to be used in an
organic EL display device.

[0070] Moreover, the crystalline semiconductor film may include a mixed
amorphous-crystalline crystal.

[0071] According to the present aspect, the crystalline semiconductor film
includes a mixed amorphous-crystalline crystal. That is, the mixed
crystal includes a crystal grain with the average size of 40 nm to 60 nm
and an amorphous area around the crystal gain. This structure can reduce
the surface roughness.

[0072] Moreover, the gate electrodes may be arranged in a row, above the
base material, and the first area included in the crystalline
semiconductor film and formed from the crystal grains with the average
size of 40 nm to 60 nm may be in a seamless belt-like shape and formed
over the area where the gate electrodes are arranged in the row.

[0073] According to the present aspect, the first area included in the
crystalline semiconductor film and formed from the crystal grains whose
average size is 40 nm to 60 nm is seamlessly formed on the area where the
gate electrodes are arranged. The substrate coated with the crystalline
semiconductor film in the present aspect can be divided into multiple
pieces along the aforementioned belt-like area according to the dicing
method or the like. Thus, the present aspect can implement the substrate
coated with the semiconductor film which can be easily divided into
multiple pieces according to the dicing method or the like.

[0074] Furthermore, the first area included in the crystalline
semiconductor film and formed from the crystal grains with the average
size of 40 nm to 60 nm is formed by: irradiating an amorphous
semiconductor film with a continuous-wave laser beam to increase a
temperature of the amorphous semiconductor film to a range of 600°
C. to 800° C., the continuous-wave laser beam having a light
intensity distribution which is continuously convex upward on each of
major and minor axes; crystallizing the amorphous semiconductor film
irradiated with the continuous-wave laser beam in the irradiating, at the
temperature increased to the range of 600° C. to 800° C.;
and increasing a crystal grain size of the crystallized amorphous
semiconductor film, as a result of an increase in an in-plane temperature
of the crystallized amorphous film to a range of 1100° C. to
1414° C. by latent heat released in the crystallizing of the
amorphous semiconductor film irradiated with the continuous-wave laser
beam, wherein the light intensity distribution continuously convex upward
is defined on the major axis to ensure a certain width of an area
included in the amorphous semiconductor film and increased in temperature
to the range of 1100° C. to 1414° C. by the latent heat,
and the area included in the amorphous semiconductor film and increased
in temperature to the range of 1100° C. to 1414° C. by the
latent heat corresponds to the first area.

[0075] According to the present aspect, the amorphous semiconductor film
is irradiated with the laser beam so that the temperature of the
amorphous semiconductor film is in the range of 600° C. to
800° C. With this irradiation, the temperature of the amorphous
semiconductor film is increased to the range of 1100° C. to
1414° C. by the latent heat, and the amorphous semiconductor film
is accordingly crystallized. Thus, the amorphous semiconductor film has
no area crystallized at a temperature higher than 1414° C. As a
result, the crystalline semiconductor film having no surface protrusions
and maintaining the surface flatness can be formed. Also, the substrate
coated with this crystalline semiconductor film can be implemented.

[0076] The thin-film transistor in an aspect according to the present
invention is a top-gate thin-film transistor including: a source-drain
electrode; a crystalline semiconductor film formed on the source-drain
electrode; an insulating film formed on the crystalline semiconductor
film; and a gate electrode formed on the insulating film, wherein the
crystalline semiconductor film is formed from crystal grains with an
average size of 40 nm to 60 nm, and each of the crystal grains are formed
by: irradiating an amorphous semiconductor film with a continuous-wave
laser beam to increase a temperature of the amorphous semiconductor film
to a range of 600° C. to 800° C., the continuous-wave laser
beam having a light intensity distribution which is continuously convex
upward on each of major and minor axes; crystallizing the amorphous
semiconductor film irradiated with the continuous-wave laser beam in the
irradiating, at the temperature increased to the range of 600° C.
to 800° C.; and increasing a crystal grain size of the
crystallized amorphous semiconductor film, as a result of an increase in
an in-plane temperature of the crystallized amorphous film to a range of
1100° C. to 1414° C. by latent heat released in the
crystallizing of the amorphous semiconductor film irradiated with the
continuous-wave laser beam, wherein the light intensity distribution
continuously convex upward is defined on the major axis to ensure a
certain width of an area included in the amorphous semiconductor film and
increased in temperature to the range of 1100° C. to 1414°
C. by the latent heat.

[0077] According to the present aspect, the amorphous semiconductor film
is irradiated with the laser beam so that the temperature of the
amorphous semiconductor film is in the range of 600° C. to
800° C. With this irradiation, the temperature of the amorphous
semiconductor film is increased to the range of 1100° C. to
1414° C. by the latent heat, and the amorphous semiconductor film
is accordingly crystallized. Thus, the amorphous semiconductor film has
no area crystallized at a temperature higher than 1414° C. As a
result, the crystalline semiconductor film having no surface protrusions
and maintaining the surface flatness can be formed. Also, the thin-film
transistor having this crystalline semiconductor film can be implemented.

[0078] The following is a description of embodiments according to the
present invention, with reference to the drawings.

First Embodiment

[0079] FIG. 1 is a diagram showing an example of a configuration of a CW
laser crystallization device in the present embodiment. FIG. 2A is a
diagram showing a minor-axis profile of a CW laser beam in the present
embodiment. FIG. 2B is a diagram showing a major-axis profile of the CW
laser beam in the present embodiment. Hereafter, the direction of the
major axis is also referred to as the "longitudinal" direction.

[0080] A CW laser crystallization device 100 shown in FIG. 1 emits a CW
laser beam onto a sample 9 which is an amorphous semiconductor, such as
an amorphous silicon layer, formed on a glass substrate. The sample 9 is
irradiated with the CW laser beam for a period of time on the order of
microseconds. The CW laser crystallization device 100 includes a laser
device 20, a major-axis formation lens 30, a mirror 40, a minor-axis
formation lens 50, a condenser lens 60, a beam profiler 70, and a quartz
glass 80.

[0081] The laser device 20 emits a CW laser beam. The laser device 20
emits, for example, a green laser light or a blue laser light for a
relatively long period of time of 10 microseconds to 100 microseconds,
instead of a short period of time of 10 nanoseconds to 100 nanoseconds.

[0082] In the CW laser crystallization device 100, the CW laser beam
emitted from the laser device 20 passes through the major-axis formation
lens 30, and a radiation direction of the CW laser beam is changed by the
mirror 40. The CW laser beam whose radiation direction has been changed
by the mirror 40 passes through the minor-axis formation lens 50, and is
collected by the condenser lens 60 to be emitted onto the sample 9. Most
of the CW laser beam collected by the condenser lens 60 passes through
the quartz glass 80 and then emitted onto the sample. However, a part of
the CW laser beam collected by the condenser lens 60 is incident upon the
beam profiler 70 where a profile of the beam is measured.

[0083] Here, the profile of the CW laser beam collected by the condenser
lens 60, that is, the profile of the CW laser beam emitted by the CW
laser crystallization device 100 has a Gaussian light intensity
distribution, as shown in FIGS. 2A and 2B. Note that each of the vertical
axes in FIGS. 2A and 2B indicates a relative intensity with respect to
the maximum intensity, represented as 100%, in the laser beam profile
shown in corresponding FIG. 2A or 2B.

[0084] The beam profile of the CW laser beam collected by the condenser
lens 60 has a Gaussian light intensity distribution on each of the minor
and major axes. This light intensity distribution results from that the
CW laser beam emitted from the laser device 20 passes through the
major-axis formation lens 30 and the minor-axis formation lens 50. It
should be noted that although the beam profile of the CW laser beam
collected by the condenser lens 60 and emitted onto the sample 9
typically has the Gaussian light intensity distribution, the present
invention is not limited to this. The profile may have any light
intensity distribution as long as the distribution is continuously convex
upward.

[0085] Here, an intensity distribution of a CW laser beam emitted from a
CW laser emitting device is basically a Gaussian distribution or
equivalent. This is why the beam profile of the CW laser beam collected
by the condenser lens 60 typically has the Gaussian light intensity
distribution on each of the minor and major axes. In other words, an
optical system of the CW laser crystallization device 100 requires no
special additional device or component. Thus, the CW laser
crystallization device 100 can relatively easily emit the CW laser beam
having the beam profile of the Gaussian light intensity distribution on
each of the minor and major axes.

[0086] The following is a description of a method to form an amorphous
semiconductor into a crystalline semiconductor by irradiating the
amorphous semiconductor with the CW laser beam for a period of time on
the order of microseconds using the CW laser crystallization device 100
configured as described. For comparison, the case of forming an amorphous
semiconductor into a crystalline semiconductor using a conventional CW
laser beam is explained as well.

[0087] Firstly, an explanation is given about the problem caused in the
case of forming the amorphous semiconductor into the crystalline
semiconductor using the conventional CW laser beam.

[0088]FIG. 3A is a diagram showing a minor-axis profile of the
conventional CW laser beam. FIG. 3B is a diagram showing a major-axis
profile of the conventional CW laser beam. FIG. 4 is a schematic diagram
explaining crystallization performed using the conventional CW laser
beam. The horizontal axis in FIG. 4 represents the passage of time. In
FIG. 4, (a) shows a section view of a beam profile of the conventional CW
laser beam in the major-axis direction. Moreover, (b) of FIG. 4 shows the
temperature distribution of a section view of the sample 9 which is an
amorphous semiconductor film. Furthermore, (c) of FIG. 4 shows a surface
state of the sample 9 which is an amorphous semiconductor film.

[0089] Here, a solid phase crystallization (SPC) range refers to a
temperature range of 600° C. to 1100° C. in which an
amorphous semiconductor film is crystallized. Note that 1100° C.
is the melting point of amorphous silicon. More specifically, SPC is a
phenomenon in which the amorphous semiconductor film is crystallized by
the solid phase growth mechanism at a temperature in the range of
600° C. to 1100° C. which is the melting point of amorphous
silicon. FIG. 5A shows an example of a silicon crystal structure
resulting from the SPC process. By the SPC process, the average grain
size of silicon crystals is approximately 30 nm, for example, as shown in
FIG. 5A and the film surface is flat.

[0090] Also, an explosive nucleation (Ex) range refers to a temperature
range of 1100° C. to 1414° C. in which an amorphous
semiconductor film is crystallized. Note that 1100° C. is the
melting point of amorphous silicon and that 1414° C. is the
melting point of silicon. More specifically, Ex is a phenomenon in which
the amorphous semiconductor film is crystallized, through a supercooled
liquid state, at a temperature in the range between 1100° C. that
is the melting point of amorphous silicon and 1414° C. that is the
melting point of silicon. FIG. 5B shows an example of a silicon crystal
structure resulting from the Ex process. By the Ex process, the average
grain size of silicon crystals is approximately 40 nm to 50 nm, for
example, as shown in FIG. 5B and the film surface is flat.

[0091] Moreover, a melting range refers a temperature range higher than
the melting point of silicon, that is, 1414° C. FIG. 5C shows an
example of a crystal structure which has been melted and then
crystallized. Crystallization of amorphous silicon in the melting range
results in polycrystalline silicon (P--Si) having the average grain size
of approximately 500 nm as shown in FIG. 5C, thereby causing protrusions
on the film surface.

[0092] As shown in FIGS. 3A and 3B, the conventional CW laser beam has the
Gaussian light intensity distribution on the minor axis and the flat-top
light intensity distribution on the major axis.

[0093] The following describes the case where the sample 9 which is an
amorphous semiconductor film is irradiated with this conventional CW
laser beam (referred to as the longitudinal flat-top CW laser beam
hereafter), with reference to FIG. 4.

[0094] Firstly, at a time t1, an amorphous semiconductor film, or more
specifically, an amorphous silicon (a-Si) film 1 is prepared as shown in
(c) of FIG. 4.

[0095] Next, at a time t2, the amorphous silicon film 1 is irradiated with
the longitudinal flat-top CW laser beam shown in (a) of FIG. 4. Here, the
longitudinal flat-top CW laser beam is continuously emitted in a beam
scan direction shown in (c) of FIG. 4. As a result, an area included in
the amorphous silicon film 1 and irradiated with the longitudinal
flat-top CW laser beam shows the temperature distribution in the SPC
range as shown in (b) of FIG. 4. It should be noted that variation in the
light intensity is caused in the flat top portion on the major axis of
the longitudinal flat-top CW laser beam shown in (a) of FIG. 4. The
variation is represented by protrusions on the flat-top portion on the
major axis in (a) of FIG. 4.

[0096] Then, at a time t3, scanning, namely, irradiation performed on the
entire upper surface of the amorphous silicon film 1 with the
longitudinal flat-top CW laser beam is completed. Here, as shown in (b)
of FIG. 4, the temperature of the amorphous semiconductor film 1
increased by the latent heat of crystallization falls approximately
within the SPC range. However, out of the amorphous semiconductor film 1,
an area irradiated with the laser beam corresponding to the protrusion
part, i.e., the laser beam having the variation in the light intensity,
increases in temperature to the Ex range exceeding the SPC range. A
crystallization mechanism is different between crystallizations performed
in the SPC range and in the Ex range exceeding the SPC range. Therefore,
the grain sizes resulting from these different crystallizations are also
different. On this account, the area crystallized in the Ex range
exceeding the SPC range has resultant variation in the crystal grain size
(referred to as the "variation in Ex" hereafter).

[0097] As described above, in the case where the amorphous semiconductor
film is formed into the crystalline semiconductor film using the
conventional longitudinal flat-top CW laser beam, the problem is that the
Ex-processed semiconductor film ends up being included in the
SPC-processed semiconductor film. That is, the variation in Ex is caused.
More specifically, not only that the surface flatness of the crystalline
semiconductor film is lost due to, for example, the protrusions on the
surface, but also that the in-plane variation is caused to the grain size
of the crystalline semiconductor film. This adversely affects the
characteristics of the thin-film transistor including this crystalline
semiconductor film.

[0098] The following describes a crystallization mechanism of silicon with
reference to the drawing. FIG. 6 is a diagram showing a relationship
between temperature and energy in silicon crystallization. In FIG. 6, the
horizontal axis represents temperature and the vertical axis represents
energy (heat).

[0099] As shown in FIG. 6, suppose that silicon in the amorphous state is
heated by, for example, laser irradiation and that the temperature of the
silicon reaches a temperature in the SPC range, namely, the range of
600° C. to 1100° C. As a result, the silicon in the
amorphous state is micro-crystallized by the solid phase growth
mechanism. Note that the average size of crystal grains in the silicon
crystallized in the SPC range in this way is from 25 nm to 35 nm.

[0100] Moreover, suppose that the silicon in the SPC range is heated so
the temperature of the silicon reaches the Ex range, i.e., reaches the
temperature which is higher than 1100° C. considered to be the
melting point where the an atomic network structure of amorphous silicon
changes and which is equal to or lower than 1414° C. that is the
melting point of silicon. As a result, the grain size is slightly
increased as compared with the size of a crystal obtained by the
solid-phase growth mechanism (i.e., the crystal size of the crystalline
silicon obtained by the SPC process). The increase in the grain size is
thought to result from the fact that the silicon is partially melted at
the temperature equal to or higher than the melting point of amorphous
silicon. Note that the average size of crystal grains in the silicon
crystallized in the Ex range in this way is from 40 nm to 60 nm.

[0101] Furthermore, suppose that the silicon in the Ex range is heated so
the temperature of the silicon reaches the melting range, that is,
reaches the temperature higher than 1414° C. which is the melting
point of silicon. As a result, crystals obtained in the Ex range (i.e.,
the crystals in the crystalline silicon obtained by the Ex process) are
exposed to heat energy as latent heat, and thus are melted (i.e., changed
into the liquid phase). Note that the silicon in the melting range is
once reduced in size in the melting process and then increased in size in
the crystallization process to be P--Si with the average grain size of 50
nm or larger.

[0102] The following describes a melting mechanism of silicon in the Ex
range. FIG. 7 is a diagram explaining a growth mechanism of an
Ex-processed crystal structure.

[0103] A plurality of atoms of silicon in the SPC range are gathered
stochastically and, when exceeding a critical grain size (i.e., 1 nm or
smaller), become a crystal nucleus in the crystal growth process.

[0104] On the other hand, atoms of silicon in the Ex range are exposed to
the temperature equal to or higher than the melting point of amorphous
silicon and thus are stimulated to move. This encourages formation of
crystal nuclei as shown in (a) of FIG. 7. Then, the latent heat melts the
perimeters of the grown nuclei, which are accordingly crystallized as
shown in (b) of FIG. 7.

[0105] In this way, the crystallization mechanism is different among the
crystallizations performed in the SPC range, in the Ex range exceeding
the SPC range, and in the melting range. Therefore, the resultant grain
size is also different for each of these crystallization mechanisms.

[0106] Here, FIG. 8 is a schematic diagram explaining crystallization
performed using the CW laser beam in the present embodiment. The
horizontal axis in FIG. 8 represents the passage of time. In FIG. 8, (a)
shows a section view of a beam profile of the CW laser beam in the
major-axis direction. Moreover, (b) of FIG. 8 shows the temperature
distribution of a section view of the sample 9 which is an amorphous
semiconductor film. Furthermore, (c) of FIG. 8 shows a surface state of
the sample 9 which is an amorphous semiconductor film.

[0107] Firstly, at a time t10, the sample 9 of an amorphous semiconductor
film, or more specifically, an amorphous silicon (a-Si) film 10 is
irradiated with the CW laser beam having a Gaussian beam profile on the
major axis as shown in (a) of FIG. 8 (this CW laser beam is referred to
as the longitudinal Gaussian CW laser beam). Here, the longitudinal
Gaussian CW laser beam is continuously emitted in a beam scan direction
shown in (c) of FIG. 8 at a power density such that the temperature of
the amorphous silicon film 10 is in the range of 600° C. to
1100° C. As a result, an SPC-processed area (shown as an SPC 11 in
FIG. 8) included in the amorphous silicon film 10 and irradiated with the
longitudinal Gaussian CW laser beam shows the temperature distribution in
the SPC range as shown in (b) of FIG. 8. It should be noted that, unlike
the longitudinal flat-top CW laser beam, the longitudinal Gaussian CW
laser beam shown in (a) of FIG. 8 has no variation in the light
intensity.

[0108] Next, at a time t11, the amorphous silicon film 10 continues to be
irradiated with the longitudinal Gaussian CW laser beam. The irradiation
using the longitudinal Gaussian CW laser beam is reaching an end of the
amorphous silicon film 10.

[0109] Here, the area included in the amorphous silicon film 10 and
irradiated with the longitudinal Gaussian CW laser beam at the time 11 is
indicated as the SPC 11, as described above. Then, the SPC 11 irradiated
with the longitudinal Gaussian CW laser beam at the time t10 is further
increased in temperature by the latent heat of crystallization and then
becomes an Ex-processed area 12 showing the temperature distribution in
the Ex range as shown in (b) of FIG. 8. At the same time, each side area
adjacent to the Ex-processed area 12 viewed in the beam scan direction is
in the SPC range to be an SPC 11 due to conduction of heat from the
Ex-processed area 12. As mentioned above, the temperature in the Ex range
refers to a temperature: which is higher than 1100° C. considered
to be the melting point that varies depending on the atomic network
structure of the amorphous silicon film 10; and which is equal to or
lower than 1414° C., i.e., the melting point of silicon.

[0110] At a time t12, scanning, namely, irradiation performed on the
entire upper surface of the amorphous silicon film 10 with the
longitudinal Gaussian CW laser beam is completed. As a result, the SPC 11
irradiated with the longitudinal Gaussian CW laser beam at the time t11
is further increased in temperature by the latent heat of crystallization
as with the above, and then becomes an Ex-processed area 12 showing the
temperature distribution in the Ex range as shown in (c) of FIG. 8. At
the same time, each side area adjacent to the Ex-processed area 12 viewed
in the beam scan direction at the time t11 is in the SPC range to be an
SPC 11 due to conduction of heat from the Ex-processed area 12.

[0111] Here, a width of the Ex-processed area 12 in a direction
perpendicular to the beam scan direction, namely, a width of the
Ex-processed area 12 in the horizontal direction, corresponds to a width
of the longitudinal Gaussian CW laser beam where a light intensity is
equal to or higher than a predetermined intensity in the major axis
direction. To be more specific, the width where the light intensity is
equal to or higher than the predetermined intensity in the major axis
direction of the longitudinal Gaussian CW laser beam refers to a width
where the power density of the longitudinal Gaussian CW laser beam is
such that the temperature of the amorphous silicon film 10 is in the
range of 600° C. to 1100° C. (namely, the SPC range).

[0112] In the case where the amorphous silicon film 10 is formed into a
crystalline silicon film using the longitudinal Gaussian CW laser beam,
the area included in the amorphous silicon film 10 and irradiated by the
width of the longitudinal Gaussian CW laser beam where the light
intensity is equal to or higher than the predetermined intensity is
crystallized into the Ex-processed crystalline silicon film. Moreover,
each side area adjacent, in the beam scan direction, to the Ex-processed
area on the amorphous silicon film 10 irradiated with the longitudinal
Gaussian CW laser beam is crystallized into the SPC-processed crystalline
silicon film. The grain size of the Ex-processed crystalline silicon
film, that is, the grain size of the crystalline silicon film having the
Ex-processed crystal structure, is slightly increased as compared with
the size of a crystal obtained by the solid phase growth mechanism, and
the uniformity is maintained as well. Moreover, no surface protrusions
are caused. The average grain size of the Ex-processed crystalline
silicon film is 40 nm to 60 nm while maintaining the in-plane uniformity.
On the other hand, the average grain size of the SPC-processed
crystalline silicon film is 25 nm to 35 nm.

[0113] As described, the amorphous semiconductor film is formed into the
crystalline semiconductor film by irradiating the amorphous semiconductor
film with the longitudinal Gaussian CW laser beam at the power density
such that the temperature of the amorphous semiconductor film is in the
range of 600° C. to 1100° C. With the irradiation using the
longitudinal Gaussian CW laser beam, the temperature of the amorphous
semiconductor film is further increased by the latent heat of
crystallization. Thus, the temperature of the amorphous semiconductor
film exceeds the temperature considered to be the melting point of
amorphous silicon that changes the atomic network structure of amorphous
silicon, and then reaches a temperature equal to or lower than
1414° C. which is the melting point of crystalline silicon.
Following this, the amorphous semiconductor film is crystallized to be
the Ex-processed crystalline semiconductor film. In this way, the
amorphous semiconductor film irradiated with the longitudinal Gaussian CW
laser beam is crystallized and has the resultant grain size slightly
increased as compared with the size of a crystal obtained by the solid
phase growth mechanism. Also, the uniformity is maintained and no surface
protrusions are caused. Here, the average crystal grain size of the
crystalline semiconductor film is 40 nm to 60 nm while maintaining the
in-plane uniformity.

[0114] At the time t10, the amorphous semiconductor film is irradiated
with the longitudinal Gaussian CW laser beam at the power density such
that the temperature of the amorphous silicon film 10 is in the range of
600° C. to 1100° C. However, the present invention is not
limited to this. The same advantageous effect can be achieved in the case
where the amorphous semiconductor film is irradiated with the
longitudinal Gaussian CW laser beam at the power density such that the
temperature of the amorphous silicon film 10 is in the range of
600° C. to 800° C.

[0115] As described thus far, the first embodiment can implement the
method of manufacturing the Ex-processed crystalline silicon film, that
is, the crystalline semiconductor film having the crystal structure with
favorable in-plane uniformity.

[0116] To be more specific, the amorphous semiconductor film is irradiated
with the longitudinal Gaussian CW laser beam for a period of time on the
order of microseconds, such as 10 microseconds to 100 microseconds, so
that the temperature of the amorphous semiconductor film is in the range
of 600° C. to 1100° C. (namely, the SPC range). As a
result, the crystalline semiconductor film having the crystal structure
with favorable in-plane uniformity can be formed. By irradiating the
amorphous semiconductor film with the longitudinal Gaussian CW laser beam
to increase the temperature of the amorphous semiconductor film into the
SPC range, the temperature of the amorphous semiconductor film stays in
the range of 1100° C. to 1414° C. by the latent heat of
crystallization. On account of this, crystallization of the irradiated
amorphous semiconductor film is performed in the range of 1100° C.
to 1414° C., instead of being performed at a temperature higher
than 1414° C. Therefore, surface protrusions can be prevented and
the surface flatness of the semiconductor film can be maintained. This
can enhance the characteristics of the thin-film transistor including the
crystalline semiconductor film formed in this way.

[0117] Also, the amorphous semiconductor film is irradiated with the
longitudinal Gaussian CW laser beam for a period of time on the order of
microseconds, instead of the order of nanoseconds. Thus, the irradiation
time of the longitudinal Gaussian CW laser beam is longer. This can
secure sufficient time for the atoms of the amorphous semiconductor film
to rearrange themselves from the amorphous state to crystallize.

[0118] Here, there may be a case where an amorphous semiconductor film is
formed into a crystalline semiconductor film by irradiating the amorphous
semiconductor film with the longitudinal Gaussian CW laser beam at a
power density such that the temperature of the irradiated amorphous
semiconductor film is instantaneously in the range of 1100° C. to
1414° C. from the very beginning. However, this is inappropriate
for the following reason. With the latent heat caused in the irradiated
area of the amorphous semiconductor film, the area is melted at the
temperature exceeding 1414° C. and then crystallized. When the
amorphous semiconductor film is crystallized after being melted at the
temperature higher than 1414° C., the amorphous semiconductor film
is once reduced in size in the melting process and then increased in size
in the crystallization process. Thus, the film may not only have a
surface protrusion identical in length to the thickness of the amorphous
semiconductor film but also have a large variation in the grain size. For
this reason, the case of irradiating, from the very beginning, the
amorphous semiconductor film with the laser beam at the power intensity
such that the temperature of the amorphous semiconductor film is
instantaneously in the range of 1100° C. to 1414° C. cannot
implement the method of manufacturing the crystalline semiconductor film
having the crystal structure with favorable in-plane uniformity. In other
words, the present case is inappropriate.

Second Embodiment

[0119] The second embodiment describes an example of the application of
the crystalline semiconductor film having the crystal structure with
favorable in-plane uniformity that is manufactured according to the
method in the first embodiment.

[0120] FIG. 9 is a diagram explaining an example of the application of the
crystalline semiconductor film to a substrate, in the present embodiment.

[0121] Firstly, a substrate coated with an amorphous semiconductor film
and a longitudinal Gaussian CW laser beam are prepared. The substrate is
configured with a base material 200 and an amorphous semiconductor film
210 which is formed on the base material 200. Here, a beam profile of the
longitudinal Gaussian CW laser beam has a Gaussian light intensity
distribution as shown in (a) of FIG. 9.

[0122] Next, the amorphous semiconductor film 210 is irradiated with the
longitudinal Gaussian CW laser beam for a period of time on the order of
microseconds. To be more specific, the amorphous semiconductor film 210
is irradiated with the longitudinal Gaussian CW laser beam so that the
temperature of the amorphous semiconductor film 210 is in the range of
600° C. to 800° C. (i.e., the SPC range).

[0123] As a result, as shown in (b) of FIG. 9, the area irradiated with
the longitudinal Gaussian CW laser beam is formed into an SPC-processed
crystalline semiconductor film 211. Here, the SPC-processed crystalline
semiconductor film 211 is a crystalline semiconductor film having a
crystal structure (or, a crystal grain) crystallized by the solid phase
growth mechanism in the SPC range of 600° C. to 1100° C.,
as described above.

[0124] At the conclusion of a predetermined elapsed time after the
completion of the irradiation using the longitudinal Gaussian CW laser
beam, an area included in the SPC-processed crystalline semiconductor
film 211 and irradiated with the longitudinal Gaussian CW laser beam is
increased in temperature to the Ex range by the latent heat of
crystallization. This results in an increase in the crystal grain size
and in an Ex-processed crystalline semiconductor film 212, as shown in
(c) of FIG. 9.

[0125] Here, a width of the Ex-processed crystalline semiconductor film
212, which is included in the SPC-processed crystalline semiconductor
film 211, corresponds to a width of the longitudinal Gaussian CW laser
beam where the light intensity is equal to or higher than a predetermined
intensity in the major axis direction.

[0126] In this way, the substrate coated with the crystalline
semiconductor film having the crystal structure with favorable in-plane
uniformity can be implemented using the longitudinal Gaussian CW laser
beam.

[0127] It should be noted that the crystalline semiconductor film having
the crystal structure with favorable in-plane uniformity that is
manufactured using the longitudinal Gaussian CW laser beam is not limited
to the above example and can be applied to a bottom-gate thin-film
transistor.

[0128] FIG. 10 is a diagram explaining a method of manufacturing a
bottom-gate thin-film transistor in the present embodiment. FIG. 11 is a
flowchart explaining the method of manufacturing the bottom-gate
thin-film transistor in the present embodiment. FIG. 12 is a diagram
showing a configuration of the bottom-gate thin-film transistor including
the crystalline semiconductor film, in the present embodiment.

[0129] Firstly, a base material 200, such as a glass substrate or an
insulating substrate, is prepared. Next, the base material 200 is cleaned
(S201), and then a contamination prevention film is formed on the base
material 200 (S202).

[0130] Then, as shown in (a) in FIG. 10, a gate electrode 220 is formed on
the base material 200 (S203). To be more specific, metal used for forming
the gate electrode 220 is deposited on the base material 200 by the
sputtering method, and then the gate electrode 220 is formed by a
patterning process such as a photolithography or etching process. For
example, the gate electrode 220 is formed from a metallic material
including: metal such as molybdenum (Mo) or Mo alloy; metal such as
titanium (Ti), aluminium (Al), or Al alloy: metal such as copper (Cu) or
Cu alloy; or metal such as silver (Ag), chromium (Cr), tantalum (Ta), or
tungsten (W).

[0131] Following this, a gate insulating film 230 is formed on the gate
electrode 220 as shown in (b) of FIG. 10, and then an amorphous
semiconductor film 240 which is, for example, an amorphous silicon film
is formed on the gate insulating film 230 as shown in (c) of FIG. 10
(S204). More specifically, in (b) of FIG. 10, the gate insulating film
230 is formed on the gate electrode 220 to cover both the base material
200 and the gate electrode 220, using a plasma chemical vapor deposition
(plasma CVD) technique. Then, in (c) of FIG. 10, the amorphous
semiconductor film 240 is seamlessly formed on the gate insulating film
230.

[0132] Next, a dehydrogenation process is performed as a preliminary
preparation for irradiating the amorphous semiconductor film with the
longitudinal Gaussian CW laser beam (S205). To be more specific,
annealing is performed at a temperature between 400° C. and
500° C. for 30 minutes. In general, the amorphous semiconductor
film 240 has a hydrogen content of 5% to 15%, as hydrogenated silicon
(Si:H). When crystallization is performed on the amorphous semiconductor
film 240 having a hydrogen content of 5% to 15%, the hydrogen interferes
with silicon and ends up inhibiting crystallization. Also, a sudden
explosive boil or the like is more likely to occur. In other words, such
an amorphous semiconductor film is undesirable for process control and,
for this reason, the dehydrogenation process is performed.

[0133] Then, the amorphous semiconductor film 240 is irradiated with the
longitudinal Gaussian CW laser beam as shown in (d) of FIG. 10, and then
the amorphous semiconductor film 240 is crystallized as shown in (e) of
FIG. 10 (S206). To be more specific, an area included in the amorphous
semiconductor film 240 and irradiated with the longitudinal Gaussian CW
laser beam by a longitudinal width where the light intensity is equal to
or higher than a predetermined intensity is formed into an Ex-processed
crystalline semiconductor film 242. Also, an area adjacent to the
EX-processed crystalline semiconductor film 242 is formed into an
SPC-processed crystalline semiconductor film 241. On the other hand, an
area included in the amorphous semiconductor film 240 and hardly
irradiated with the longitudinal Gaussian CW laser beam remains as the
amorphous semiconductor film 240. Here, the longitudinal width of the
longitudinal Gaussian CW laser beam where the light intensity is equal to
or higher than the predetermined intensity is wider than at least a width
of the gate electrode 220 (i.e., the width in a direction perpendicular
to the longitudinal direction of the CW laser beam). The irradiation
method using the longitudinal Gaussian CW laser beam has been explained
in detail above and, therefore, the explanation is not repeated here.

[0134] Next, a hydrogen plasma process is performed (S207). More
specifically, a hydrogen termination process is performed, via this
hydrogen plasma process, on the amorphous semiconductor film 240
irradiated with the longitudinal Gaussian CW laser beam. That is to say,
the hydrogen termination process is performed on the amorphous
semiconductor film 240, the SPC-processed crystalline semiconductor film
241, and the Ex-processed crystalline semiconductor film 242.

[0135] Following this, a semiconductor film 250 is formed (S208). To be
more specific, the semiconductor film 250 is formed on the amorphous
semiconductor film 240, the SPC-processed crystalline semiconductor film
241, and the Ex-processed crystalline semiconductor film 242, using the
plasma CVD technique. Then, the patterning process is performed in such a
way to keep the Ex-processed crystalline semiconductor film 242 as it is,
and the etching process is performed to remove a part of the
semiconductor film 250 and the remaining amorphous semiconductor film 240
and SPC-processed semiconductor film 241. As a result, only the
crystalline semiconductor film having the crystal structure with
favorable in-plane uniformity can be formed as a channel part of the
bottom-gate thin-film transistor.

[0136] Next, a source-drain electrode 270 is formed (S210). More
specifically, metal used for forming the source-drain electrode 270 is
deposited on the semiconductor film 250 by the sputtering method.
Following this, the patterning process is performed to form the
source-drain electrode 270. Here, the semiconductor film 250 serves as an
ohmic contact layer connecting the Ex-processed crystalline semiconductor
film 242 and the source-drain electrode 270.

[0137] In this way, the bottom-gate thin-film transistor shown in FIG. 12
is manufactured.

[0138] It should be noted that although the method of manufacturing a
single bottom-gate thin-film transistor has been described for
convenience of explanation, the present invention is not limited to this.
A plurality of bottom-gate thin-film transistors may be manufactured at
one time.

[0139]FIG. 13 is a diagram explaining the case where the plurality of
bottom-gate thin-film transistors are manufactured at one time.

[0140] In the case where the plurality of bottom-gate thin-film
transistors are manufactured at one time, a plurality of gate electrodes
220 are formed on the base material 200 at predetermined intervals and
the gate insulating film 230 is formed over these gate electrodes 220, in
S201 to S205 described above. Here, the gate electrodes 220 may be
arranged at the predetermined intervals in a row, and such rows may also
be arranged at predetermined intervals. FIG. 13 shows the latter case as
an example.

[0141] Then, in S206, an area which is included in the amorphous
semiconductor film 240 and positionally corresponds to the gate
electrodes 220 arranged at the predetermined intervals in a row is
continuously irradiated with the longitudinal Gaussian CW laser beam, as
shown in FIG. 13. Hereafter, this area of the amorphous semiconductor
film 240 is referred to as the belt-like area. Thus, the belt-like area
of the amorphous semiconductor film 240 is crystallized. Here, a
longitudinal width of the longitudinal Gaussian CW laser beam where the
light intensity is equal to or higher than a predetermined intensity is
wider than a width of the belt-like area of the amorphous semiconductor
film 240. Note that the width of the belt-like area of the amorphous
semiconductor film 240 refers to a width in a direction perpendicular to
the scan direction of the longitudinal Gaussian CW laser beam.

[0142] As described, the belt-like area included in the amorphous
semiconductor film 240 is continuously irradiated with the longitudinal
Gaussian CW laser beam. Here, the area where the gate electrodes 220 are
arranged at the predetermined intervals positionally corresponds to the
belt-like area whose width is wider than each width of the gate
electrodes 220 in the direction perpendicular to the arrangement
direction of the gate electrodes 220. As a result of the irradiation, the
belt-like area which positionally corresponds to the gate electrodes 220
can be formed into an Ex-processed crystalline semiconductor film 242.
Also, as with the above, an area adjacent to the EX-processed crystalline
semiconductor film 242 in the direction perpendicular to the scan
direction of the longitudinal Gaussian CW laser beam is formed into an
SPC-processed crystalline semiconductor film 241.

[0143] In this way, the width of the Gaussian CW laser beam in the major
axis direction matches with the width of the belt-like area which is
included in the amorphous semiconductor film and positionally corresponds
to the gate electrodes arranged at the predetermined intervals. Thus, the
belt-like area can be selectively irradiated, out of the amorphous
semiconductor film. Accordingly, the area included in the crystalline
semiconductor film and formed as a channel part of the thin-film
transistor can be selectively micro-crystallized. In addition, the
crystalline semiconductor film having a flat surface can be formed.

[0144] It should be noted that the Ex-processed crystalline semiconductor
film 242 is formed from crystal grains whose average size is 40 nm to 60
nm, and is also formed in the shape of a belt covering the area which
positionally corresponds to the gate electrodes 220 arranged at the
predetermined intervals in a row. Moreover, the SPC-processed crystalline
semiconductor film 241 is formed adjacent to the Ex-processed crystalline
semiconductor film 242. The base material 200 including this crystalline
semiconductor film has an advantageous effect of being easily divided
into multiple pieces along the aforementioned belt-like area according to
the dicing method or the like.

[0145] As described thus far, the second embodiment can implement: the
bottom-gate thin-film transistor to which the crystalline semiconductor
film having the crystal structure with favorable in-plane uniformity is
applied; and the substrate coated with the crystalline semiconductor
film.

Third Embodiment

[0146] In the second embodiment, the bottom-gate thin-film transistor and
the substrate coated with the crystalline semiconductor film are
described as the application examples. The third embodiment describes a
top-gate thin-film transistor as an application example.

[0147]FIG. 14 is a diagram explaining a method of manufacturing the
top-gate thin-film transistor in the present embodiment. FIG. 15 is a
diagram showing a configuration of the top-gate thin-film transistor in
the present embodiment.

[0148]FIG. 14 shows a part of the process of manufacturing the top-gate
thin-film transistor.

[0149] More specifically, (b) in FIG. 14 shows a manufacturing process of
forming a source-drain electrode 310 on a base substrate 300 and then
forming an amorphous semiconductor film 320 on the source-drain electrode
310. Following this, the amorphous semiconductor film 320 is irradiated
with a longitudinal Gaussian CW laser beam shown in (a) of FIG. 14, and
is then crystallized as shown in (c) of FIG. 14.

[0150] To be more specific, out of the amorphous semiconductor film 320,
an area which is to be a gate is irradiated with the longitudinal
Gaussian CW laser beam by a longitudinal width where the light intensity
is equal to or higher than a predetermined intensity.

[0151] As a result, the area included in the amorphous semiconductor film
320 and irradiated with the longitudinal Gaussian CW laser beam by the
longitudinal width where the light intensity is equal to or higher than
the predetermined intensity is formed into an Ex-processed crystalline
semiconductor film 322. Also, an area adjacent to the EX-processed
crystalline semiconductor film 322 is formed into an SPC-processed
crystalline semiconductor film 321. On the other hand, an area included
in the amorphous semiconductor film 320 and hardly irradiated with the
longitudinal Gaussian CW laser beam remains as the amorphous
semiconductor film 320. The details of the irradiation method using the
longitudinal Gaussian CW laser beam are the same as those explained above
and, therefore, the explanation is not repeated here.

[0152] Accordingly, the top-gate thin-film transistor having the
Ex-processed crystalline semiconductor film 322, as shown in FIG. 15 as
an example, can be formed. The top-gate thin-film transistor shown in
FIG. 15 includes the base material 300, the source-drain electrode 310,
the Ex-processed crystalline semiconductor film 322, a gate insulating
film 340 formed on the Ex-processed crystalline semiconductor film 322,
and a gate electrode 350 formed on the gate insulating film 340.

[0153] The configuration of the top-gate thin-film transistor is not
limited to the one shown in FIG. 15, and may be the one shown in FIG. 16
for example. FIG. 16 is a diagram showing another configuration of a
top-gate thin-film transistor in the third embodiment. In FIG. 16,
components identical to those in FIG. 15 are assigned the same numerals
as used in FIG. 15. It should be noted that, in FIG. 15, a protection
film 460 formed on the gate electrode 350 of the top-gat thin-film
transistor is illustrated.

[0154]FIG. 17 is a flowchart explaining the method of manufacturing the
top-gate thin-film transistor in the present embodiment.

[0155] Processes S301 to S311 are identical to the processes S201 to S209,
except for the order in which the source-drain electrode 310 and the gate
electrode 350 are formed. Also, a process performed in S305 has been
explained with reference to FIG. 14 and, thus, the explanation is omitted
here. It should be noted that, in S312, a protection film such as the
protection film 460 is formed on the gate electrode 350.

[0156] Also, it should be obvious that the top-gate thin-film transistor
in each of FIGS. 16 and 17 in the present embodiment may be manufactured
in multiple at one time as in the case of the second embodiment. In this
case, a plurality of source-drain electrodes 310 are formed on the base
substrate 300 at predetermined intervals and the gate insulating film 340
is formed over the gate electrodes 350, in S301 to S303. Here, the
source-drain electrodes 310 may be arranged at the predetermined
intervals in a row, and such rows may also be arranged at predetermined
intervals.

[0157] Then, an area (i.e., a belt-like area) which is included in the
amorphous semiconductor film and positionally corresponds to the gate
electrodes 350 formed between the source-drain electrodes 310 arranged at
the predetermined intervals is continuously irradiated with the
longitudinal Gaussian CW laser beam. As a result, out of the amorphous
semiconductor film, the belt-like area which positionally corresponds to
the gate electrodes 350 can be formed into an EX-processed crystalline
semiconductor film 322.

[0158] It should be noted that the Ex-processed crystalline semiconductor
film 322 is formed from crystal grains whose average size is 40 nm to 60
nm, and is also formed in the shape of a belt covering the area where the
gate electrodes 350 are arranged at the predetermined intervals in a row.
Moreover, the SPC-processed crystalline semiconductor film 321 is formed
adjacent to the Ex-processed crystalline semiconductor film 322. The base
material 300 including this crystalline semiconductor film has an
advantageous effect of being easily divided into multiple pieces along
the aforementioned belt-like area according to the dicing method or the
like.

[0159] As described thus far, the third embodiment can implement the
top-gate thin-film transistor to which the crystalline semiconductor film
having the crystal structure with favorable in-plane uniformity is
applied.

[0160] As described above, the amorphous semiconductor film is irradiated
with the CW laser beam having the Gaussian distributions in the
directions of the major and minor axes so that the temperature of the
amorphous semiconductor film is in the range of 600° C. to
800° C. (i.e., the SPC range). Then, the temperature of the
amorphous semiconductor film reaches the range of 1100° C. to
1414° C. (i.e., the Ex range) by the latent heat. After this, the
amorphous semiconductor film is crystallized. This method causes no area
in the amorphous semiconductor film that is crystallized after exceeding
1414° C. (that is, the melting range). Thus, the crystalline
semiconductor film having no surface protrusions and maintaining the
surface flatness can be formed. In this way, not only the crystalline
semiconductor film having no surface protrusions and maintaining the
surface flatness can be formed, but also the thin-film transistor having
this crystalline semiconductor film can be implemented.

[0161] According to the present invention described thus far, the
amorphous semiconductor film is irradiated with the CW laser beam having
a longitudinal light intensity gradient, such as a Gaussian distribution,
for a period of time on the order of microseconds. As a result of this
irradiation, the amorphous semiconductor film is crystallized. Here,
using the latent heat effect, the amorphous semiconductor film is
crystallized in the temperature range between the melting point of the
amorphous semiconductor film and the crystalline melting point. With
this, in-plane variation in the grain size of the formed crystalline
semiconductor film is prevented, and also the grain size of the crystal
structure is increased as compared with the size of a crystal obtained by
the solid phase growth mechanism. Thus, the present invention can provide
the method of manufacturing the crystalline semiconductor film having the
crystal structure with favorable in-plane uniformity, the method of
manufacturing the substrate coated with the crystalline semiconductor
film, and the thin-film transistor.

[0162] Also, the crystalline semiconductor film including the Ex-processed
crystal structure which is superior to the SPC-processed crystal
structure in electrical characteristics and which has a microcrystal
structure with favorable in-plane uniformity can be formed. This can
implement a thin-film transistor with less characteristic variation and a
display device using this thin-film transistor.

[0163] The average size of crystal grains in the Ex-processed crystalline
semiconductor film is 40 nm to 60 nm. On this account, a top-gate
thin-film transistor manufactured using such an Ex-processed crystalline
semiconductor film has an advantageous effect of securing the mobility to
obtain adequate ON characteristics as the thin-film transistor to be used
for an organic EL display device.

[0164] It should be noted that the crystalline semiconductor film may be
formed only from an Ex-processed crystalline semiconductor film or may be
formed from mixed amorphous and Ex-processed crystals. In such a case,
the crystalline semiconductor film includes a mixed amorphous-crystalline
crystal. That is, the mixed crystal includes a crystal grain with the
average size of 40 nm to 60 nm and an amorphous area around the crystal
gain. Such an amorphous structure can reduce crystallographic
unconformity at an interface between adjacent crystal grains of the
crystalline semiconductor film.

[0165] Although the method of manufacturing the crystalline semiconductor
film, the method of manufacturing the substrate coated with the
crystalline semiconductor film, and the thin-film transistor according to
the present invention have been described on the basis of the above
embodiments, the present invention is not limited to these embodiments.
It should be obvious that changes and modifications conceived by those
skilled in the art may be appropriately made to each of the embodiments
and that the features of the embodiments may be appropriately combined.
Therefore, as long as these changes, modifications, and combinations do
not depart from the spirit of the present invention, they are intended to
be included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

[0166] The present invention can be used for a method of manufacturing a
crystalline semiconductor film, a method of manufacturing a substrate
coated with a crystalline semiconductor film, and a thin-film transistor.
In particular, the present invention can be used for forming a channel
part of a thin-film transistor in an organic EL display device used as a
flat panel display (FPD) device, such as a TV.